[Mesa-dev] [PATCH 0/3] Use GitLab CI to build Mesa

[Juan A. Suarez Romero]

Hello.

This is a first part of a more complete proposal to use GitLab CI to build and
test Mesa. This first part just adds the required pieces to build Mesa, using the
different supported tools (meson, autotools, and scons).

A second part, to be sent in the future, will use the results of the former to
run different tests and verify everything works fine.

An example of the pipeline that will result from this patchset can be seen at
https://gitlab.freedesktop.org/jasuarez/mesa/pipelines/3070.

I hope I can explain here all the rationale behind this proposal. Any question
is welcomed.


## Brief introduction

This proposal is based on a setup we are using at Igalia for the different
releases we were in charge of. The idea is to build different Docker images
containing Mesa with different setups; thus we are build an image using Meson,
another using Autotools, and so on. Even more, as the Gallium drivers depend on
the LLVM version, we also use different setups with different LLVM versions.

Some of those images are later used to run different test suites in different
hardware. So we just save those Docker images for further pulling in a next step
in the pipeline. For those that we are not using for testing, we plainly discard
them. At least, they helped to verify that the setup builds correctly.

A very complete example of this setup pipeline can be seen in
https://gitlab.com/igalia/graphics/mesa/pipelines/26539728

As said before, right now we are just focusing on building the images, rather
than testing them. In a second part to be sent we will focus on the testing.


## Why Docker

When we started the initial setup, we have something clear: just build
everything once, and tests as in many devices as possible. The reasons are
different: we have powerful machines for building, but then for testing we have
different hosts with different power skills; some low-end NUCS, some with few
memory, and so on. And also, we wanted to ensure that the discrepancies when
testing were not due the different software configuration (different distros,
different versions, different installed packages, ...): use the same software as
much as possible. And then we have another requirement: have an easy way to
distribute the result in the testing machines.

And Containers is something that really helps to achive this. And inside
Containers, Docker is a de-facto, so we started to use Docker. Wich Docker, we
can build self-contained images with everything we need to run Mesa, and
distribute it very easily. And the fact that it allows to use layers to build
the images, makes quite easy to reuse previous results in the future builds.


## Why Rocker

As said before, Docker is a great tool, but it has a couple of drawbacks when
building the images.

On one side, the Dockerfile syntax is quite rigid, and does not allow for
complex configuration. For instance, it's quite difficult to create a Dockerfile
where you can allow to use Meson or Autotools to build Mesa, specified as
parameter when building the image. Either you create an unreadable Dockerfile,
or ends up creating different Dockerfiles, even when most of them shares a lot
of common code. And if you start to add more options, like LLVM version, it
becomes crazy.

One way to solve this problem is to create a Dockerfile with templates, like
Jinja or any similar tool, and then generate the final Dockerfile with the
proper options.

The other problem with Docker, more complex to build, is how to allow to
cache. We are using ccache to speed up the build time, but the problem is that
Docker does not allow to mount external directories when building an image. And
thus, we can't reuse the cache generated in previous builds. There are some
proposals like creating different images, or building the image using `docker
run` (which allows to mount those directories) plus `docker commit` to generate
the final image. But all of them leads to Dockerfiles quite difficult to
maintain. So solution is normally just not use cache, with the impact this has.

In our case, we solved both problems using Rocker instead of Docker. Rocker is
like a `docker build` with steroids, that fixes the above problems. It is a tool
that is able to create Docker images based on Rockerfiles, that are like
Dockerfiles but with enriched syntax, that provides the same power as a
template. And, which is more important, allows to mount external directories
when building the image; we use this feature to mount the ccache results
directory.

Unfortunately, Rocker is a tool that is not maintained anymore
(https://github.com/grammarly/rocker). We still use it because it provides
everything we need, and fortunately we don't need any more features.

Maybe there are other alternatives out there, but we were happy with this and
hence our proposal. If we want to use Docker rather than Rocker, then we could
use template tools like Jinja, and forget about caching during build, which will
impact on the build time.


## Involved stages

The dependencies required to build Mesa doesn't change very frequently, so
building them everytime is a waste of time. As Docker allows to create images
based on the content of other images, we have defined the setup in several
stages.

On a first stage a "base" image is built. This image contains almost all the
dependencies required to build Mesa. Worth to mention that libdrm is excluded
here, as this is a dependency that really changes quite frequently, so we
postpone the installation for further stages.

One we have the "base" image, we create different images with the different LLVM
compilers. This ensure that when using a specific image we only have that LLVM
version, and not any other.

An important point here is that, these builts appears in the pipeline, they are
not actually built if not required. That is, in the case of the base image, if
the Rockerfile used to create the image has changed with respect to the one used
to create the image that is already in the registry, then the image is rebuilt
(as this means something changed, very likely some dependency). But if the
Rockerfile didn't change, then there is no need to rebuild the image, and just
keep using the one already in the registry. This is also done for the LLVM
images. This helps to improve the speed, as most of the times they don't need to
be built again.

The third stage is the one that builds Mesa itself. Here we just define which
tool to use and which LLVM version. This is done by passing the right parameters
to the `rocker build` tool. It will pick the right base image, install the
missing dependencies (mainly, libdrm), select which drivers should be built
(based on the LLVM version and parsing the configure.ac file), and create the
image.

As LLVM version only affects the Gallium drivers, and in order to reduce the
build time, we added a fake tool "gallium" that just builds only the Gallium
drivers based on the LLVM version.

Another worth to mention point is the `distcheck` tool. As it names suggests,
this run `make distcheck` to build Mesa, which basically creates a dist tarball,
uncompress it, and builds it with autotools. The bad part is that it only builds
the dist tarball with autotools, but it does not checks with the other tools
(scons and meson). To fix this, this `distcheck` job generates as an artifact
the dist tarball, which is used by the "Tarball" stage in the pipeline (4th
stage) to uncompress and builds using those tools.

Finally, at this moment we only save one of the images created, the one
corresponding to the `autotools` jobs, as this has all the drivers built, and
can be downloaded and used for testing. The other ones are just used to verify
that everything is built correctly, but discarded afterwards.


Juan A. Suarez Romero (3):
  gitlab-ci: build Mesa using GitLab CI
  gitlab-ci: build base images if dependencies changed
  gitlab-ci: Build from the released tarballs

 .gitlab-ci.yml                    | 204 ++++++++++++++++++++++++++++++
 gitlab-ci/Rockerfile.base         | 201 +++++++++++++++++++++++++++++
 gitlab-ci/Rockerfile.llvm         |  59 +++++++++
 gitlab-ci/Rockerfile.mesa         | 145 +++++++++++++++++++++
 gitlab-ci/inspect-remote-image.sh |  21 +++
 5 files changed, 630 insertions(+)
 create mode 100644 .gitlab-ci.yml
 create mode 100644 gitlab-ci/Rockerfile.base
 create mode 100644 gitlab-ci/Rockerfile.llvm
 create mode 100644 gitlab-ci/Rockerfile.mesa
 create mode 100755 gitlab-ci/inspect-remote-image.sh

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